It consists of a set of massive box beams that roll on tracks and which themselves support one or more moving trolleys running up and down the beams. I say "they" because of course one had to be a qualified member of a crew to operate one of these behemoths, one person on the floor able to hook and unhook the load communicating to the crane operator up in a mobile cab by means of international hand signals:

They did let us use small cranes to move detector components around a bit, but nothing in the multi-ton scale.

It would be a daring piece of industrial home design to put a bridge crane into a living space. Since the crane itself has to transit along rails, a large open room without interior walls would be optimal. It would be especially useful when one wished to move a grand piano from place to place (say around a sunken living room), though it might be possible to dream up some other use cases. I imagine that one could stack one's Costco purchases on an attractively designed pallet out by the carport, then hoist them up and over to the pantry area (the garbage and recyclables would make the return trip, of course).